WO 2011/101019 A1 describes an impeller-type coolant pump with an outlet valve arrangement in the root of an outlet channel. The outlet valve arrangement is provided with a valve flap whereby the pivot axis of the valve flap is arranged at one end of the flap body and is provided in the surface plane of the valve seat. The valve flap should be pivotable even at high rotational speeds of the pump rotor at which a high fluid pressure against the valve flap either in a closing direction or in an opening direction can occur. High actuation power is needed, however, to provide full functionality at all rotational speeds.